The microstructural changes and low-temperature tensile properties of ultra-low carbon steel aged at 443 K were examined, and the relationship between the low-temperature tensile properties and ultra-low carbon state was discussed. Fine cementites of approximately 60 nm were observed at 0.6 ks and coarsened to approximately 800 nm at 600 ks. The yield and tensile stresses at 77 K increased until 6 ks and then decreased. The nominal stress-strain curves of all the specimens at 77 K exhibited low elastic limits, the nominal stress plateaued from an approximate nominal strain of 0.002 and, subsequently, work hardening occurred. In the unaged and 6 ks aged specimens, several twins were generated after the elastic limit, and which increased dramatically in the nominal stress plateau regime, and corresponded to macroscopic yielding. In contrast, the number of twins in the 600 ks aged specimen negligibly increased during macroscopic yielding. Macroscopic yielding occurred in the unaged and 6 ks aged specimens by deformation twinning, while in the 600 ks aged specimen it occurred by slip deformation. In the 6 ks aged specimen, the fine cementites and/or decrease in solid solute carbon enhanced the critical resolved shear stresses of deformation twinning, resulting in the highest strength. In the 600 ks aged specimen, the coarse cementites negligibly enhanced the critical resolved shear stress for slip deformation. Hence, the strength of the specimen aged for 600 ks decreased as compared to the specimen aged for 6 ks, and slip deformation occurred.

考察了443 K时效超低碳钢的显微组织变化和低温拉伸性能，探讨了低温拉伸性能与超低碳状态的关系。在 0.6 ks 观察到大约 60 nm 的细渗碳体，并在 600 ks 粗化到大约 800 nm。77 K 时的屈服应力和拉伸应力增加到 6 ks，然后下降。所有试样在 77 K 下的标称应力-应变曲线显示出低弹性极限，标称应力从大约 0.002 的标称应变稳定下来，随后发生加工硬化。在未时效和 6 ks 时效试样中，在弹性极限后产生了几个孪晶，并且在名义应力平台状态下急剧增加，并对应于宏观屈服。相比之下，600 ks 老化试样中的双胞胎数量在宏观屈服期间可以忽略不计。未时效和 6 ks 时效试样通过变形孪生发生宏观屈服，而 600 ks 时效试样发生滑动变形。在 6 ks 时效试样中，细小的渗碳体和/或固体溶质碳的减少增强了变形孪晶的临界解析剪应力，从而产生了最高的强度。在 600 ks 时效试样中，粗渗碳体对滑动变形的临界解析剪切应力的增强可以忽略不计。因此，与时效 6 ks 的试样相比，时效 600 ks 的试样强度下降，并发生滑动变形。未时效和 6 ks 时效试样通过变形孪生发生宏观屈服，而 600 ks 时效试样发生滑动变形。在 6 ks 时效试样中，细小的渗碳体和/或固体溶质碳的减少增强了变形孪晶的临界解析剪应力，从而产生了最高的强度。在 600 ks 时效试样中，粗渗碳体对滑动变形的临界解析剪切应力的增强可以忽略不计。因此，与时效 6 ks 的试样相比，时效 600 ks 的试样强度下降，并发生滑动变形。未时效和 6 ks 时效试样通过变形孪生发生宏观屈服，而 600 ks 时效试样发生滑动变形。在 6 ks 时效试样中，细小的渗碳体和/或固体溶质碳的减少增强了变形孪晶的临界解析剪应力，从而产生了最高的强度。在 600 ks 时效试样中，粗渗碳体对滑动变形的临界解析剪切应力的增强可以忽略不计。因此，与时效 6 ks 的试样相比，时效 600 ks 的试样强度下降，并发生滑动变形。细小的渗碳体和/或固体溶质碳的减少增强了变形孪晶的临界解析剪切应力，从而导致最高强度。在 600 ks 时效试样中，粗渗碳体对滑动变形的临界解析剪切应力的增强可以忽略不计。因此，与时效 6 ks 的试样相比，时效 600 ks 的试样强度下降，并发生滑动变形。细小的渗碳体和/或固体溶质碳的减少增强了变形孪晶的临界解析剪切应力，从而导致最高强度。在 600 ks 时效试样中，粗渗碳体对滑动变形的临界解析剪切应力的增强可以忽略不计。因此，与时效 6 ks 的试样相比，时效 600 ks 的试样强度下降，并发生滑动变形。